Inter-α-trypsin Inhibitor, a Covalent Protein-Glycosaminoglycan-Protein Complex
2004; Elsevier BV; Volume: 279; Issue: 37 Linguagem: Inglês
10.1074/jbc.r300039200
ISSN1083-351X
AutoresLisheng Zhuo, Vincent Hascall, Koji Kimata,
Tópico(s)Carbohydrate Chemistry and Synthesis
ResumoThe inter-α-trypsin inhibitor (IαI) 1The abbreviations used are: IαI, inter-α-trypsin inhibitor; UTI, urinary trypsin inhibitor; PαI, pre-α inhibitor; HC, heavy chain of IαI family molecules; PGP, protein-glycosaminoglycan-protein covalent complex; SHAP, serum-derived hyaluronan-associated protein; HA, hyaluronan; CS, chondroitin sulfate; TSG6 or TNFIP6, tumor necrosis factor-stimulated gene 6. family, a typical and classical example for protein-glycosaminoglycan-protein (PGP) complexes, occurs constitutively in plasma at relatively high concentrations and is a result of alternate combinations of three kinds of heavy chains with a common light chain, the bikunin proteoglycan. The family is characterized by the unique covalent linkage between the heavy chains and the chondroitin sulfate chain of bikunin. The early studies on the IαI family molecules have largely focused on the light chain (bikunin) that is fully responsible for their protease inhibitory activity. Since the mid-1980s, the structures of the family molecules have been clarified, and this led to the discovery of their complex interaction with another glycosaminoglycan, hyaluronan (HA), generating the serum-derived hyaluronan-associated protein (SHAP)-HA complex. Research from various directions has clarified many aspects of the biological function of the PGP complexes and provides a new vista on their interesting structure-function relationships, especially on their roles in inflammation. The IαI family was first identified as a trypsin inhibitor activity in nephropathic and pneumonopathic urine in 1909 and in normal urine in 1910. One member, the urinary trypsin inhibitor (UTI), was purified much later in the 1950s (1Shulman N.R. J. Biol. Chem. 1955; 213: 655-671Abstract Full Text PDF PubMed Google Scholar, 2Astrup T. Alkjoer K. Soardi F. Scand. J. Clin. Lab. Invest. 1959; 11: 181Crossref Scopus (17) Google Scholar) when it was independently isolated by researchers working on mucopolysaccharides, leukemia, and urolithiasis and was given many names: acid-stable protease inhibitor, prealbumin-like protease inhibitor, urinastatin, HI30, mingin, EDC1, uronic acid-rich protein, and nephrocalin (3Anderson A.J. Maclagan N.F. Biochem. J. 1955; 59: 638-644Crossref PubMed Scopus (19) Google Scholar, 4Chawla R.K. Wadsworth A.D. Rudman D. J. Immunol. 1978; 121: 1636-1639PubMed Google Scholar, 5Atmani F. Mizon J. Khan S.R. Eur. J. Biochem. 1996; 236: 984-990Crossref PubMed Scopus (52) Google Scholar). Based on the presence of two tandem Kunitz-type protease inhibitory domains, a structure-based name, bikunin, was suggested in 1990 to avoid confusion (6Gebhard W. Hochstrasser K. Fritz H. Enghild J.J. Pizzo S.V. Salvesen G. Biol. Chem. Hoppe Seyler. 1990; 371: 13-22PubMed Google Scholar). It is now known that bikunin (Mr ∼ 40,000) is a proteoglycan with a chondroitin sulfate (CS) chain and is the predominant protease inhibitor in urine. Bikunin is acid- and heat-stable and has an acidic pI between 2 and 3 largely due to the presence of sialic acid and CS. There were continuous efforts to find a serum cognate based on a hypothesis that UTI has a serum origin. In the 1970s, this led to the identification of serum IαI (7Proksch G.J. Lane J. Nordschow C.D. Clin. Biochem. 1973; 6: 200-206Crossref PubMed Scopus (27) Google Scholar), a macromolecule previously purified in the 1960s (8Heide K. Heimburger N. Haupt H. Clin. Chim. Acta. 1965; 11: 82Crossref Scopus (55) Google Scholar) (Fig. 1). Conclusive evidence for the identity came from the comparison of amino acid sequences in the 1980s (9Wachter E. Hochstrasser K. Hoppe Seyler's Z. Physiol. Chem. 1981; 362: 1351-1355Crossref PubMed Scopus (93) Google Scholar). Smaller components with inhibitor activity were released when IαI was treated in vitro in acidic conditions or with proteases, such as plasmin, trypsin, and elastase (10Dietl T. Dobrinski W. Hochstrasser K. Hoppe Seyler's Z. Physiol. Chem. 1979; 360: 1313-1318Crossref PubMed Scopus (54) Google Scholar, 11Pratt C.W. Pizzo S.V. Biochemistry. 1987; 26: 2855-2863Crossref PubMed Scopus (22) Google Scholar), or when incubated with inflammatory cells, in particular neutrophils, or cancer cells (12Pratt C.W. Swaim M.W. Pizzo S.V. J. Leukocyte Biol. 1989; 45: 1-9Crossref PubMed Scopus (30) Google Scholar, 13Kobayashi H. Gotoh J. Hirashima Y. Terao T. J. Biol. Chem. 1996; 271: 11362-11367Abstract Full Text Full Text PDF PubMed Scopus (47) Google Scholar). Cognate molecules with lower molecular weights were also found in serum, pre-α inhibitor (PαI), and inter-α-like trypsin inhibitor (14Enghild J.J. Thogersen I.B. Pizzo S.V. Salvesen G. J. Biol. Chem. 1989; 264: 15975-15981Abstract Full Text PDF PubMed Google Scholar). IαI was thought to be a single polypeptide chain until molecular biology techniques became available. Cell-free translation of liver mRNAs (15Bourguignon J. Vercaigne D. Sesboue R. Martin J.P. Salier J.P. FEBS Lett. 1983; 162: 379-383Crossref PubMed Scopus (30) Google Scholar) and subsequent cloning (16Diarra-Mehrpour M. Bourguignon J. Sesboue R. Mattei M.G. Passage E. Salier J.P. Martin J.P. Eur. J. Biochem. 1989; 179: 147-154Crossref PubMed Scopus (73) Google Scholar) indicated that IαI contains "heavy" and "light" polypeptides encoded by distinct genes. Reviews in 1990 summarized the multipeptide chain structure and defined the IαI family (6Gebhard W. Hochstrasser K. Fritz H. Enghild J.J. Pizzo S.V. Salvesen G. Biol. Chem. Hoppe Seyler. 1990; 371: 13-22PubMed Google Scholar, 17Salier J.P. Trends Biochem. Sci. 1990; 15: 435-439Abstract Full Text PDF PubMed Scopus (119) Google Scholar). IαI family molecules are encoded by at least five genes, ITIH1–ITIH4 for the four heavy chains (HCs) and AMBP for the light chain (the core protein of bikunin). Interestingly, the AMBP gene encodes both the core protein and a functionally unrelated serum protein, α1-microglobulin, as a precursor fusion protein (18Kaumeyer J.F. Polazzi J.O. Kotick M.P. Nucleic Acids Res. 1986; 14: 7839-7850Crossref PubMed Scopus (190) Google Scholar). cDNAs of the four HCs show high sequence homology except in the C-terminal one-third of HC4 (19Chan P. Risler J.L. Raguenez G. Salier J.P. Biochem. J. 1995; 306: 505-512Crossref PubMed Scopus (51) Google Scholar). The multipeptide structure of IαI was masked by its unusual PGP structure in which the polypeptide subunits are covalently linked together via a CS chain (20Enghild J.J. Salvesen G. Hefta S.A. Thogersen I.B. Rutherfurd S. Pizzo S.V. J. Biol. Chem. 1991; 266: 747-751Abstract Full Text PDF PubMed Google Scholar). In 1981, the UTI carbohydrates were identified as: (a) an O-linked, GalNAc-rich chain attached to serine at position 10 and (b) an N-linked oligosaccharide at position 45 (21Hochstrasser K. Schonberger O.L. Rossmanith I. Wachter E. Hoppe Seyler's Z. Physiol. Chem. 1981; 362: 1357-1362Crossref PubMed Scopus (77) Google Scholar). Chondroitinase and testicular hyaluronidase digestion of IαI and PαI identified the O-glycan as a low sulfated CS chain (22Balduyck M. Mizon C. Loutfi H. Richet C. Roussel P. Mizon J. Eur. J. Biochem. 1986; 158: 417-422Crossref PubMed Scopus (44) Google Scholar, 23Ochiai H. Toyoda H. Onodera M. Shinbo A. Shinomiya K. Imanari T. Chem. Pharm. Bull. (Tokyo). 1988; 36: 3726-3727Crossref PubMed Scopus (9) Google Scholar) and separated the HCs and bikunin (14Enghild J.J. Thogersen I.B. Pizzo S.V. Salvesen G. J. Biol. Chem. 1989; 264: 15975-15981Abstract Full Text PDF PubMed Google Scholar, 24Jessen T.E. Faarvang K.L. Ploug M. FEBS Lett. 1988; 230: 195-200Crossref PubMed Scopus (76) Google Scholar). The CS linkage to bikunin is a typical O-xylosylserine (22Balduyck M. Mizon C. Loutfi H. Richet C. Roussel P. Mizon J. Eur. J. Biochem. 1986; 158: 417-422Crossref PubMed Scopus (44) Google Scholar). Analyses also identified the novel ester bond that links the α-carboxyl of C-terminal aspartates of the HCs with C-6 hydroxyl groups of internal GalNAcs in the CS chain (20Enghild J.J. Salvesen G. Hefta S.A. Thogersen I.B. Rutherfurd S. Pizzo S.V. J. Biol. Chem. 1991; 266: 747-751Abstract Full Text PDF PubMed Google Scholar, 25Enghild J.J. Salvesen G. Thogersen I.B. Valnickova Z. Pizzo S.V. Hefta S.A. J. Biol. Chem. 1993; 268: 8711-8716Abstract Full Text PDF PubMed Google Scholar) (Fig. 1). The amino acid sequence at the CS attachment site in bikunin, Glu-Gly-Ser-Gly, is well conserved among all species examined. The CS chain is relatively short (Mr ∼ 8000), with 12–18 disaccharide repeats (GlcUAβ1,3-GalNAcβ1,4-) and a conventional linkage region (GlcUAβ1–3Galβ1–3Galβ1–4Xylβ1)-O-Ser (26Toyoda H. Kobayashi S. Sakamoto S. Toida T. Imanari T. Biol. Pharm. Bull. 1993; 16: 945-947Crossref PubMed Scopus (40) Google Scholar, 27Enghild J.J. Thogersen I.B. Cheng F. Fransson L.A. Roepstorff P. Rahbek-Nielsen H. Biochemistry. 1999; 38: 11804-11813Crossref PubMed Scopus (63) Google Scholar). About 30% of the GalNAc, usually those near the linkage region, are sulfated at C-4 hydroxyl groups (27Enghild J.J. Thogersen I.B. Cheng F. Fransson L.A. Roepstorff P. Rahbek-Nielsen H. Biochemistry. 1999; 38: 11804-11813Crossref PubMed Scopus (63) Google Scholar). CS chains synthesized during inflammations are shorter with decreased sulfation (28Capon C. Mizon C. Lemoine J. Rodie-Talbere P. Mizon J. Biochimie (Paris). 2003; 85: 101-107Crossref PubMed Scopus (28) Google Scholar). In the electron microscope, bikunin appears as a small sphere (diameter of ∼2 nm), whereas HCs have an N-terminal globule (diameter of ∼11 nm) with a thin tail (length of ∼15.5 nm) attached to the bikunin sphere (29Blom A.M. Morgelin M. Oyen M. Jarvet J. Fries E. J. Biol. Chem. 1999; 274: 298-304Abstract Full Text Full Text PDF PubMed Scopus (46) Google Scholar). The two HCs of human IαI are located close to each other in the less sulfated region of the CS chain (27Enghild J.J. Thogersen I.B. Cheng F. Fransson L.A. Roepstorff P. Rahbek-Nielsen H. Biochemistry. 1999; 38: 11804-11813Crossref PubMed Scopus (63) Google Scholar). The HCs on IαI vary from species to species. Typically, human IαI contains HC1 and HC2 (14Enghild J.J. Thogersen I.B. Pizzo S.V. Salvesen G. J. Biol. Chem. 1989; 264: 15975-15981Abstract Full Text PDF PubMed Google Scholar), bovine IαI contains HC2 and HC3 (30Castillo G.M. Templeton D.M. FEBS Lett. 1993; 318: 292-296Crossref PubMed Scopus (49) Google Scholar), and rodent IαI contains both types (31Yamamoto T. Yamamoto K. Sinohara H. J. Biochem. (Tokyo). 1996; 120: 145-152Crossref PubMed Scopus (12) Google Scholar). On the other hand, the single HC in PαI is HC3 in all species examined except for bovine PαI, which contains HC2 (30Castillo G.M. Templeton D.M. FEBS Lett. 1993; 318: 292-296Crossref PubMed Scopus (49) Google Scholar). Low levels of HC2/bikunin (inter-α-like trypsin inhibitor) and HC1/bikunin are found in human serum, which seem to be degraded forms of IαI (14Enghild J.J. Thogersen I.B. Pizzo S.V. Salvesen G. J. Biol. Chem. 1989; 264: 15975-15981Abstract Full Text PDF PubMed Google Scholar, 25Enghild J.J. Salvesen G. Thogersen I.B. Valnickova Z. Pizzo S.V. Hefta S.A. J. Biol. Chem. 1993; 268: 8711-8716Abstract Full Text PDF PubMed Google Scholar). Currently, neither the reason nor the mechanism for the selectivity of HCs is known. Although IαI family genes are expressed in various tissues (32Mizushima S. Nii A. Kato K. Uemura A. Biol. Pharm. Bull. 1998; 21: 167-169Crossref PubMed Scopus (28) Google Scholar), the circulating IαI family molecules are produced principally by the liver. Interestingly, bikunin and HC cDNA cotransfection shows that cells other than hepatocytes, COS cells, also can couple a HC with the bikunin proteoglycan (33Blom A.M. Thuveson M. Fries E. Biochem. J. 1997; 328: 185-191Crossref PubMed Scopus (14) Google Scholar). Bikunin is first synthesized in fusion with α1-microglobulin (34Lindqvist A. Bratt T. Altieri M. Kastern W. Akerstrom B. Biochim. Biophys. Acta. 1992; 1130: 63-67Crossref PubMed Scopus (74) Google Scholar), and the cleavage occurs in the trans-Golgi after adding the CS and HCs (35Bratt T. Olsson H. Sjoberg E.M. Jergil B. Akerstrom B. Biochim. Biophys. Acta. 1993; 1157: 147-154Crossref PubMed Scopus (64) Google Scholar). The connecting tetrapeptide (Arg-X1-X2-Arg) conforms to a consensus sequence recognized by the intracellular endoprotease family that includes furin. However, furin does not seem to be responsible for the cleavage (36Brat T. Cedervall T. Akerstrom B. FEBS Lett. 1994; 354: 57-61Crossref PubMed Scopus (23) Google Scholar). The HCs undergo several proteolytic steps during biosynthesis. The signal and following N-terminal propeptides (19Chan P. Risler J.L. Raguenez G. Salier J.P. Biochem. J. 1995; 306: 505-512Crossref PubMed Scopus (51) Google Scholar) are removed in the endoplasmic reticulum, probably by a Golgi enzyme in transit (37Thuveson M. Fries E. J. Biol. Chem. 1999; 274: 6741-6746Abstract Full Text Full Text PDF PubMed Scopus (17) Google Scholar, 38Thogersen I.B. Enghild J.J. J. Biol. Chem. 1995; 270: 18700-18709Abstract Full Text Full Text PDF PubMed Scopus (53) Google Scholar). The large C-terminal extension (240–280 amino acid residues beginning with the conserved sequence Pro-His-Phe-Ile-Ile) is released when the remainder of the HC is coupled to the CS (Fig. 2) (19Chan P. Risler J.L. Raguenez G. Salier J.P. Biochem. J. 1995; 306: 505-512Crossref PubMed Scopus (51) Google Scholar). Therefore, the assembly of a HC involves two likely coordinated steps: a cleavage of the Asp-Pro bond and then the formation of the ester bond (38Thogersen I.B. Enghild J.J. J. Biol. Chem. 1995; 270: 18700-18709Abstract Full Text Full Text PDF PubMed Scopus (53) Google Scholar). The C-terminal extension seems to be required for the formation of the ester linkage (37Thuveson M. Fries E. J. Biol. Chem. 1999; 274: 6741-6746Abstract Full Text Full Text PDF PubMed Scopus (17) Google Scholar). No protease with specificity toward the conserved sequence around the cleavage site has been described. As their original names suggest, the family molecules were studied extensively as protease inhibitors. Bikunin exhibits a weak inhibitory activity against proteases including trypsin, chymotrypsin, neutrophil elastase, and plasmin (39Potempa J. Kwon K. Chawla R. Travis J. J. Biol. Chem. 1989; 264: 15109-15114Abstract Full Text PDF PubMed Google Scholar). However, none has been defined as a physiological target of bikunin, which questions whether protease inhibition is a major function of IαI family molecules. Although circulating levels are high (150–500 μg/ml), they account for only ∼5% of the total protease inhibitory activity of the plasma, and the Ki values of bikunin are not low enough to be effective at physiological concentrations (39Potempa J. Kwon K. Chawla R. Travis J. J. Biol. Chem. 1989; 264: 15109-15114Abstract Full Text PDF PubMed Google Scholar). Proteases that bikunin inhibits are often more efficiently inhibited by their respective physiological inhibitors (40Odum L. Dan. Med. Bull. 1991; 38: 68-77PubMed Google Scholar). Accordingly, on the basis of clearance of injected bikunin-protease complexes, it was proposed that the IαI family functions as a shuttle that traps proteases and then transfers them to physiological inhibitors (41Pratt C.W. Pizzo S.V. Arch. Biochem. Biophys. 1986; 248: 587-596Crossref PubMed Scopus (18) Google Scholar). However, bikunin inhibits plasmin on the surfaces of cancer cells more efficiently than plasmin in solution, in contrast to α2-macroglobulin and α1-inhibitor, which may relate to the antimetastatic effect of bikunin (42Kobayashi H. Shinohara H. Takeuchi K. Itoh M. Fujie M. Saitoh M. Terao T. Cancer Res. 1994; 54: 844-849PubMed Google Scholar). In addition, bikunin may also inhibit granzyme K, the lymphocyte granule-stored serine protease that is implicated in T-cell- and natural killer cell-mediated cytotoxic defense after recognition of target cells (43Wilharm E. Parry M.A. Friebel R. Tschesche H. Matschiner G. Sommerhoff C.P. Jenne D.E. J. Biol. Chem. 1999; 274: 27331-27337Abstract Full Text Full Text PDF PubMed Scopus (65) Google Scholar). Trypstatin, an inhibitor of chymase secreted by peritoneal mast cells, was suggested to be a processed fragment of bikunin that the cells had taken up from the circulation (44Itoh H. Ide H. Ishikawa N. Nawa Y. J. Biol. Chem. 1994; 269: 3818-3822Abstract Full Text PDF PubMed Google Scholar). Other diverse activities, particularly pharmaceutical effects, of bikunin have been described, such as mitogenic activity, inhibitory activity toward hyaluronidase, prevention from premature delivery, ischemia stress and renal failure, and suppression of pancreatitis, colitis, and arthritis, for which various mechanisms have been proposed (for review, see Ref. 45Fries E. Blom A.M. Int. J. Biochem. Cell Biol. 2000; 32: 125-137Crossref PubMed Scopus (152) Google Scholar). The above studies focused on the bikunin portion of IαI family molecules. However, more than 90% of circulating bikunin carries HCs, whereas urinary bikunin is predominantly free of HCs (46Slota A. Sjoquist M. Wolgast M. Alston-Smith J. Fries E. Biol. Chem. Hoppe Seyler. 1994; 375: 127-133Crossref PubMed Scopus (17) Google Scholar). Furthermore, free bikunin has a much shorter half-life in circulation (4 min in mice) than that of HC-bikunin complexes (several hours in mice) (47Zhuo L. Yoneda M. Zhao M. Yingsung W. Yoshida N. Kitagawa Y. Kawamura K. Suzuki T. Kimata K. J. Biol. Chem. 2001; 276: 7693-7696Abstract Full Text Full Text PDF PubMed Scopus (228) Google Scholar, 48Sugiki M. Sumi H. Maruyama M. Yoshida E. Mihara H. Enzyme. 1989; 42: 31-38Crossref PubMed Scopus (25) Google Scholar). This paradox is explained by recent studies of IαI-HA interactions. Soon after its discovery in the 1960s, IαI was found to have an association with HA (49Hamerman D. Sandson J. J. Clin. Invest. 1963; 42: 1882-1889Crossref PubMed Scopus (15) Google Scholar, 50Sandson J. Hamerman D. Schwick G. Trans Assoc. Am. Physicians. 1965; 78: 304-313PubMed Google Scholar). HA is the major glycosaminoglycan in synovial fluid that is responsible for its viscoelastic properties and joint-lubricating function. HA isolated from knee joints of patients with active rheumatoid arthritis or chronic gout contained more firmly bound protein (∼10%) than HA from normal knee joints (∼2%). Immunodiffusion with specific antibodies identified the protein as IαI then thought to be a single protein (50Sandson J. Hamerman D. Schwick G. Trans Assoc. Am. Physicians. 1965; 78: 304-313PubMed Google Scholar). The pathological HA preparations had altered properties, such as gel formation, electrophoretic immobility, and extremely rapid sedimentation in the ultracentrifuge at pH 4.5, suggesting an aggregation of the protein-HA complex (50Sandson J. Hamerman D. Schwick G. Trans Assoc. Am. Physicians. 1965; 78: 304-313PubMed Google Scholar). These investigators proposed that IαI entered the diseased joint from serum and became firmly bound to HA, thereby altering its properties (50Sandson J. Hamerman D. Schwick G. Trans Assoc. Am. Physicians. 1965; 78: 304-313PubMed Google Scholar, 51Becker A. Sandson J. Arthritis Rheum. 1971; 14: 764-766Crossref PubMed Scopus (15) Google Scholar). These pioneering findings were neglected except in a report in 1988 that confirmed the pathological association of IαI with synovial HA and further showed that the complex was more resistant to degradation by oxygen-derived free radicals (52Hutadilok N. Ghosh P. Brooks P.M. Ann. Rheum. Dis. 1988; 47: 377-385Crossref PubMed Scopus (58) Google Scholar). In 1990, a protein of ∼85 kDa was found firmly associated with HA in the extracellular matrix of cultured mouse dermal fibroblasts (53Yoneda M. Suzuki S. Kimata K. J. Biol. Chem. 1990; 265: 5247-5257Abstract Full Text PDF PubMed Google Scholar). The protein was not metabolically labeled and therefore was derived from the serum added to the culture. It was designated SHAP and was identified as the HCs of the IαI family molecules (54Huang L. Yoneda M. Kimata K. J. Biol. Chem. 1993; 268: 26725-26730Abstract Full Text PDF PubMed Google Scholar). The term SHAP is used below for HCs in HA complexes. The SHAP-HA complexes were then isolated from synovial fluid and from preovulatory follicular fluid (55Jessen T.E. Odum L. Johnsen A.H. Biol. Chem. Hoppe Seyler. 1994; 375: 521-526Crossref PubMed Scopus (46) Google Scholar). Mass spectrometry showed that SHAPs are bound to HA by an ester bond between carboxyl groups of the aspartates at their C termini and the C-6 hydroxyl groups of internal N-acetylglucosamines in HA, analogous to the original HC ester bond to CS in IαI (56Zhao M. Yoneda M. Ohashi Y. Kurono S. Iwata H. Ohnuki Y. Kimata K. J. Biol. Chem. 1995; 270: 26657-26663Abstract Full Text Full Text PDF PubMed Scopus (149) Google Scholar) (Fig. 1). Because several SHAPs are linked to one HA molecule, the SHAP-HA complex is a second PGP covalent complex. The analogous linkage structures in the SHAP-HA complex and IαI suggest that the SHAP-HA complex is formed by a transesterification of HCs from CS to HA, accompanied by the release of bikunin proteoglycan (Fig. 2). SHAP-HA complex formed when HA and IαI were incubated with serum at 37 °C (53Yoneda M. Suzuki S. Kimata K. J. Biol. Chem. 1990; 265: 5247-5257Abstract Full Text PDF PubMed Google Scholar, 56Zhao M. Yoneda M. Ohashi Y. Kurono S. Iwata H. Ohnuki Y. Kimata K. J. Biol. Chem. 1995; 270: 26657-26663Abstract Full Text Full Text PDF PubMed Scopus (149) Google Scholar). No HC transfer was observed at low temperature or when divalent cations were absent, indicating the presence of an as yet unidentified enzymatic factor (53Yoneda M. Suzuki S. Kimata K. J. Biol. Chem. 1990; 265: 5247-5257Abstract Full Text PDF PubMed Google Scholar, 54Huang L. Yoneda M. Kimata K. J. Biol. Chem. 1993; 268: 26725-26730Abstract Full Text PDF PubMed Google Scholar). HC transfer activity has also been detected in follicular fluid and in media conditioned by follicular granulosa cells, hepatoma cells, or glioma cells (57Chen L. Zhang H. Powers R.W. Russell P.T. Larsen W.J. J. Biol. Chem. 1996; 271: 19409-19414Abstract Full Text Full Text PDF PubMed Scopus (98) Google Scholar, 58Odum L. Andersen C.Y. Jessen T.E. Reproduction. 2002; 124: 249-257Crossref PubMed Scopus (19) Google Scholar). 2L. Zhuo, V. C. Hascall, and K. Kimata, unpublished observations. Recently, tumor necrosis factor stimulated gene-6 product (TSG6, also named TNFIP6) has been identified as a candidate because it interacts with both HA through its link module (59Lee T.H. Wisniewski H.G. Vilcek J. J. Cell Biol. 1992; 116: 545-557Crossref PubMed Scopus (260) Google Scholar) and IαI (60Wisniewski H.G. Burgess W.H. Oppenheim J.D. Vilcek J. Biochemistry. 1994; 33: 7423-7429Crossref PubMed Scopus (99) Google Scholar). Furthermore, TSG6-null mice exhibit the same phenotype as bikunin-null mice, namely inability to form the SHAP-HA complex and hence to form the expanded HA-based matrix of the cumulus oöphorus during ovulation, with resulting female infertility (47Zhuo L. Yoneda M. Zhao M. Yingsung W. Yoshida N. Kitagawa Y. Kawamura K. Suzuki T. Kimata K. J. Biol. Chem. 2001; 276: 7693-7696Abstract Full Text Full Text PDF PubMed Scopus (228) Google Scholar, 61Fulop C. Szanto S. Mukhopadhyay D. Bardos T. Kamath R.V. Rugg M.S. Day A.J. Salustri A. Hascall V.C. Glant T.T. Mikecz K. Development. 2003; 130: 2253-2261Crossref PubMed Scopus (331) Google Scholar). Interestingly, recombinant TSG6 forms an ∼120-kDa complex with IαI, in which TSG6 appears to replace a HC on the CS (60Wisniewski H.G. Burgess W.H. Oppenheim J.D. Vilcek J. Biochemistry. 1994; 33: 7423-7429Crossref PubMed Scopus (99) Google Scholar). This complex was present in arthritic synovial fluid and air pouch exudates (62Wisniewski H.G. Hua J.C. Poppers D.M. Naime D. Vilcek J. Cronstein B.N. J. Immunol. 1996; 156: 1609-1615PubMed Google Scholar). Although it was suggested that TSG6 acts as an enhancing factor rather than as the transfer activity per se (63Jessen T.E. Odum L. Reproduction. 2003; 125: 27-31Crossref PubMed Scopus (50) Google Scholar), recent work has shown that TSG6 can displace HC from IαI to form a TSG6-HC complex in solution that can in turn form a SHAP-HA complex when HA or HA oligosaccharides are added (64Mukhopadhyay D. Asari A. Rugg M.S. Day A.J. Fulop C. J. Biol. Chem. 2004; 279: 11119-11128Abstract Full Text Full Text PDF PubMed Scopus (54) Google Scholar). Further, PG-M/versican, a HA-binding proteoglycan with two tandem link modules, enhances the formation of the SHAP-HA complex in solution (65Yoneda M. Zhao M. Zhuo L. Watanabe H. Yamada Y. Huang L. Nagasawa S. Nishimura H. Shinomura T. Isogai Z. Kimata K. Abatangelo G. Weigel P.H. New Frontiers in Medical Sciences: Redefining Hyaluronan. Elsevier Science B.V., Amsterdam2000: 21-30Google Scholar). In the pre-ovulatory mammalian follicle, the oocyte is closely surrounded by ∼1000 cumulus cells in a compact cumulus cell-oocyte complex. After an ovulatory stimulus, the follicle becomes permeable to serum, introducing IαI, and the cumulus cells begin to synthesize HA and organize it into an extensive extracellular matrix, causing a dramatic increase in cell-oocyte complex volume (cumulus oöphorus expansion). Compact cell-oocyte complexes expand in vitro when incubated in the presence of follicle-stimulating hormone and serum. In the absence of serum, HA is synthesized but not organized into a matrix. The necessary serum factor was identified as IαI, and it was suggested that the mechanism involved a direct ionic interaction between IαI and HA (66Chen L. Mao S.J. McLean L.R. Powers R.W. Larsen W.J. J. Biol. Chem. 1994; 269: 28282-28287Abstract Full Text PDF PubMed Google Scholar). However, the interaction was weak at physiological ionic strength, questioning its ability to maintain the matrix structure. Further, HA isolated from ovarian follicular fluid contained HCs, but no bikunin, indicating that a SHAP-HA complex is formed (55Jessen T.E. Odum L. Johnsen A.H. Biol. Chem. Hoppe Seyler. 1994; 375: 521-526Crossref PubMed Scopus (46) Google Scholar, 60Wisniewski H.G. Burgess W.H. Oppenheim J.D. Vilcek J. Biochemistry. 1994; 33: 7423-7429Crossref PubMed Scopus (99) Google Scholar, 64Mukhopadhyay D. Asari A. Rugg M.S. Day A.J. Fulop C. J. Biol. Chem. 2004; 279: 11119-11128Abstract Full Text Full Text PDF PubMed Scopus (54) Google Scholar). Serum from the bikunin-null mouse contains unprocessed HCs, but they are not able to form the SHAP-HA complex (47Zhuo L. Yoneda M. Zhao M. Yingsung W. Yoshida N. Kitagawa Y. Kawamura K. Suzuki T. Kimata K. J. Biol. Chem. 2001; 276: 7693-7696Abstract Full Text Full Text PDF PubMed Scopus (228) Google Scholar). Consequently, homozygous null female mice are defective in cumulus oöphorus expansion, with greatly reduced oocyte ovulation and subsequent infertility. Fertilization was rescued by intraperitoneal administration of purified IαI but not by bikunin alone (47Zhuo L. Yoneda M. Zhao M. Yingsung W. Yoshida N. Kitagawa Y. Kawamura K. Suzuki T. Kimata K. J. Biol. Chem. 2001; 276: 7693-7696Abstract Full Text Full Text PDF PubMed Scopus (228) Google Scholar). Incubation of bikunin proteoglycan with serum from homozygous null mice also failed to couple it with the unprocessed HCs, consistent with the fact that the assembly of IαI is completed in the Golgi apparatus of hepatocytes (35Bratt T. Olsson H. Sjoberg E.M. Jergil B. Akerstrom B. Biochim. Biophys. Acta. 1993; 1157: 147-154Crossref PubMed Scopus (64) Google Scholar). These results suggest a novel concept for the function of bikunin proteoglycan, i.e. to provide a CS chain to form an ester bond with HCs for their subsequent transfer to HA. TSG6 synthesis is also up-regulated in cumulus cells and in surrounding granulosa cells in the preovulatory follicle (67Fulop C. Kamath R.V. Li Y. Otto J.M. Salustri A. Olsen B.R. Glant T.T. Hascall V.C. Gene (Amst.). 1997; 202: 95-102Crossref PubMed Scopus (109) Google Scholar, 68Mukhopadhyay D. Hascall V.C. Day A.J. Salustri A. Fulop C. Arch. Biochem. Biophys. 2001; 394: 173-181Crossref PubMed Scopus (106) Google Scholar). Further, hyaluronidase digestion of the expanded cumulus oöphorus identified covalent TSG6-SHAP-HA complexes as well as SHAP-HA complexes in the expanded matrix, whereas bikunin was absent (68Mukhopadhyay D. Hascall V.C. Day A.J. Salustri A. Fulop C. Arch. Biochem. Biophys. 2001; 394: 173-181Crossref PubMed Scopus (106) Google Scholar). Conversely, hyaluronidase digestion of ovaries from the TSG6-null mouse revealed a complete absence of SHAP-HA complexes (61Fulop C. Szanto S. Mukhopadhyay D. Bardos T. Kamath R.V. Rugg M.S. Day A.J. Salustri A. Hascall V.C. Glant T.T. Mikecz K. Development. 2003; 130: 2253-2261Crossref PubMed Scopus (331) Google Scholar). Thus, TSG6 is essential for the transesterification of HCs from IαI in organizing the expanded cumulus oöphorus matrix. The TSG6-SHAP-HA complex provides a possible mechanism for stabilizing the matrix by cross-linking HA between the non-covalent TSG6-HA interaction, mediated by the link module in TSG6, and the covalent cross-link of its HA-SHAP partner. IαI family molecules also exert matrix-stabilizing effects on cultured human fibroblasts, on human mesothelial cells (69Blom A. Pertoft H. Fries E. J. Biol. Chem. 1995; 270: 9698-9701Abstract Full Text Full Text PDF PubMed Scopus (68) Google Scholar), and on mouse mammary carcinoma cells (70Zhao M. Yoneda M. Zhuo L. Huang L. Watanabe H. Yamada Y. Nagasawa S. Nishimura H. Kimata K. Kennedy J.F. Phillips G.O. Williams P.A. Hascall V.C. Hyaluronan. 1. Woodhead Publishing Ltd., Cambridge2002: 497-500Google Scholar), likely through SHAP-HA complexes. HA and IαI normally distribute in different body compartments, connective tissues and the circulation, respectively. Their convergence under various abnormal conditions, such as malignancy and inflammation, and during some physiological processes, such as ovulation, is associated with increased bikunin levels in urine (71Faarvang H.J. Scand. J. Clin. Lab. Invest. 1965; 17: 1-78Crossref PubMed Scopus (8) Google Scholar). Therefore, the function of the interactions involving IαI and HA is of general relevance. Rheumatoid Arthritis—The synovium, a highly vascularized tissue lacking a basement membrane-like structure, allows synoviocyte-secreted HA to enter the joint cavity where it is a major component of the synovial fluid. An inflamed synovium is the most likely site for the formation of the synovial SHAP-HA complex. Indeed, the SHAP-HA complex was detected within the synovial cavity at a concentration far higher than that in the circulation (72Kida D. Yoneda M. Miyaura S. Ishimaru T. Yoshida Y. Ito T. Ishiguro N. Iwata H. Kimata K. J. Rheumatol. 1999; 26: 1230-1238PubMed Google Scholar, 73Yingsung W. Zhuo L. Morgelin M. Yoneda M. Kida T. Watanabe H. Ishiguro N. Iwata H. Kimata K. J. Biol. Chem. 2003; 278: 32710-32718Abstract Full Text Full Text PDF PubMed Scopus (93) Google Scholar). The complex from rheumatoid arthritic synovial fluid is heterogeneous in HA chain length and in the SHAP-to-HA molecular ratio: a HA chain of ∼2 MDa carries 3–5 SHAP proteins on average (73Yingsung W. Zhuo L. Morgelin M. Yoneda M. Kida T. Watanabe H. Ishiguro N. Iwata H. Kimata K. J. Biol. Chem. 2003; 278: 32710-32718Abstract Full Text Full Text PDF PubMed Scopus (93) Google Scholar). Some altered properties of pathological synovial HA, such as gelation at low pH and rapid sedimentation upon ultracentrifugation (49Hamerman D. Sandson J. J. Clin. Invest. 1963; 42: 1882-1889Crossref PubMed Scopus (15) Google Scholar, 50Sandson J. Hamerman D. Schwick G. Trans Assoc. Am. Physicians. 1965; 78: 304-313PubMed Google Scholar), and the ability to form a macromolecular aggregate (73Yingsung W. Zhuo L. Morgelin M. Yoneda M. Kida T. Watanabe H. Ishiguro N. Iwata H. Kimata K. J. Biol. Chem. 2003; 278: 32710-32718Abstract Full Text Full Text PDF PubMed Scopus (93) Google Scholar) may relate to the presence of SHAPs. These results and those discussed below suggest that the SHAP-HA complex has a role in the inflammatory response by regulating adhesion of infiltrating leukocytes. Inflammatory Bowel Disease—Crohn's disease and ulcerative colitis are the major chronic inflammatory diseases of the gastrointestinal tract and are often referred to as inflammatory bowel disease. The major pathological changes include an increase in intestinal mucosal mononuclear leukocytes and a dramatic hyperplasia of the smooth muscle cells of the muscularis mucosae. The etiology of inflammatory bowel disease is multifactorial including viral infection. The interaction between inflamed smooth muscle cells and recruited leukocytes is also important in the development and propagation of this disease. Studies in vitro showed that viral infection of human colon smooth muscle cells or treatment with the virus mimetic polyinosinic acid:polycytidylic acid up-regulated the production of HA and the formation of extracellular HA "cable" structures (74De La Motte C.A. Hascall V.C. Drazba J. Bandyopadhyay S.K. Strong S.A. Am. J. Pathol. 2003; 163: 121-133Abstract Full Text Full Text PDF PubMed Scopus (274) Google Scholar) (Fig. 2). The cable structures were specifically formed in the presence of serum, and the SHAP-HA complex was found in the structure (74De La Motte C.A. Hascall V.C. Drazba J. Bandyopadhyay S.K. Strong S.A. Am. J. Pathol. 2003; 163: 121-133Abstract Full Text Full Text PDF PubMed Scopus (274) Google Scholar). Cell adhesion assays revealed that peripheral mononuclear cells or histiocytic lymphoma U937 monocytic cells bound specifically to the cables via a mechanism involving in part CD44, a HA receptor, on their surface. Therefore, a highly organized structure, involving the SHAP-HA complex, may be required for the leukocytes to adhere and potentially to subsequently activate. Serum Levels of the SHAP-HA Complex—It is generally accepted that HA is partially degraded at local sites and carried by lymph to the lymph nodes where a large portion is endocytosed and degraded. However, a significant portion is also carried to the general circulation and rapidly cleared by liver sinusoidal endothelial cells. The daily turnover of HA is in the order of 10–100 mg whereas the level in circulation is maintained at only about 30–40 ng/ml in healthy individuals (75Laurent T.C. Acta Otolaryngol. Suppl. 1987; 442: 7-24Crossref PubMed Scopus (220) Google Scholar). However, under pathological conditions, up-regulated production, impaired uptake, and/or decreased degradation cause dramatic elevation of serum HA. Clinically, the level is used to aid diagnosis and to monitor progress in cases of rheumatoid arthritis and liver cirrhosis (76Laurent T.C. Laurent T.C. The Chemistry, Biology and Medical Applications of Hyaluronan and Its Derivatives. Portland Press, London1998: 305-314Google Scholar). An enzyme-linked immunosorbent assay method, developed for measuring the level of the SHAP-HA complex in serum and other humoral sources (72Kida D. Yoneda M. Miyaura S. Ishimaru T. Yoshida Y. Ito T. Ishiguro N. Iwata H. Kimata K. J. Rheumatol. 1999; 26: 1230-1238PubMed Google Scholar), has revealed a significant correlation between the levels of HA and SHAP in diseases with elevated serum HA (72Kida D. Yoneda M. Miyaura S. Ishimaru T. Yoshida Y. Ito T. Ishiguro N. Iwata H. Kimata K. J. Rheumatol. 1999; 26: 1230-1238PubMed Google Scholar, 73Yingsung W. Zhuo L. Morgelin M. Yoneda M. Kida T. Watanabe H. Ishiguro N. Iwata H. Kimata K. J. Biol. Chem. 2003; 278: 32710-32718Abstract Full Text Full Text PDF PubMed Scopus (93) Google Scholar) 2L. Zhuo, V. C. Hascall, and K. Kimata, unpublished observations. and provides further evidence for the formation of the SHAP-HA complex in these pathological conditions. For a long period, studies on IαI family molecules focused on bikunin, the protease inhibitor, with the impression that the HCs only modified the function of bikunin. After the SHAP-HA complex was identified in 1990, a matrix-stabilizing role of IαI family molecules was observed, and its biological relevance was established with mouse models in 2001. These studies provide a novel concept for the role of each domain of IαI, i.e. the HCs are directly related to the physiological function of IαI through transfer to HA, and their coupling to bikunin is necessary for the transesterification reaction. It is now important to find if other partners interact with the HCs in addition to HA, TSG6, and PG-M/versican (64Mukhopadhyay D. Asari A. Rugg M.S. Day A.J. Fulop C. J. Biol. Chem. 2004; 279: 11119-11128Abstract Full Text Full Text PDF PubMed Scopus (54) Google Scholar, 70Zhao M. Yoneda M. Zhuo L. Huang L. Watanabe H. Yamada Y. Nagasawa S. Nishimura H. Kimata K. Kennedy J.F. Phillips G.O. Williams P.A. Hascall V.C. Hyaluronan. 1. Woodhead Publishing Ltd., Cambridge2002: 497-500Google Scholar). Characterization of potentially functional motifs in the HC polypeptide, such as those suggested by sequence homology (19Chan P. Risler J.L. Raguenez G. Salier J.P. Biochem. J. 1995; 306: 505-512Crossref PubMed Scopus (51) Google Scholar), will also be useful. Finally, the mechanisms for forming the HC-CS bond in IαI in the Golgi of hepatocytes and for the transesterification to form the SHAP-HA counterpart needed to be defined in both normal processes such as TSG6-mediated cumulus oöphorus expansion, and in pathological processes such as rheumatoid arthritis and inflammatory bowel disease. We are very much indebted to people who have been involved in this research.
Referência(s)